1. Field of the Invention
The present invention relates generally to a method of acquiring uplink synchronization for a mobile WiMax system analyzer and, more particularly, to an uplink synchronization acquisition method using the mobile WiMax system analyzer, which enable the mobile WiMax system analyzer to acquire and analyze the uplink synchronization of a Portable Subscriber Station (PSS) using a predetermined test mode, provided to the PSS, without requiring a Radio Access Station (RAS).
2. Description of the Related Art
Currently, methods of wirelessly accessing the Internet include a method of accessing the Internet via a mobile telephone network based on a Wireless Application Protocol (WAP) or Wireless Internet Platform for Interoperability (WIPI), and a method of accessing the Internet via a public wireless Local Area Network (LAN) and an Access Point (AP). However, the method using a mobile telephone network has fundamental limitations on use as a universal Internet access method due to the limited screen size, the limited input interface, and a billing system based on a measured rate system. Meanwhile, the method using a wireless LAN has fundamental problems in that it can only be used within a range having a radius of tens of meters around an AP, and in that it also realizes poor mobility. In order to overcome such problems, mobile WiMax (or WiBro, which is a subset of mobile WiMax and a Korean mobile WiMax standard) system has been proposed as wireless Internet service capable of enabling high-speed Internet access at ADSL-level quality and cost, either when at rest or in intermediate-speed motion.
FIG. 1 is a diagram illustrating a method of allocating resources along a time axis and a frequency axis in Orthogonal Frequency Division Multiple Access (OFDMA). In general communication systems, since radio resources, that is, time and frequency, are limited, they must be allocated to a plurality of PSS users and used by them. Meanwhile, unlike existing CDMA-based systems and Wireless LAN (WLAN) systems, mobile WiMax system employ OFDMA, in which a two-dimensional resource region, defined by the time axis and the frequency axis, is allocated to respective PSSs, as shown in FIG. 1.
FIG. 2 is a diagram showing the MAP structure of a mobile WiMax system. As shown in FIG. 2, in the mobile WiMax system, a plurality of pieces of data using the same channel coding method and modulation method is sent in a batch in order to improve efficiency. A set of data regions using the same channel coding method and modulation method is referred to as a “burst.” The location and size information of each burst can be seen from the MAP information of a frame, as shown in FIG. 2. Here, the term ‘frame’ refers to a structured data sequence having a fixed duration, which is used in the Physical Layer (PHY) standard. A single frame may include both Downlink (hereinafter abbreviated as “DL”; a link from an RAS to a PSS) and Uplink (hereinafter abbreviated as “UL”; a link from a PSS to an RAS) sub-frames.
Since the mobile WiMax system employs TDD, in which UL transmission and DL transmission share the same frequency but are performed at different times, essential information, including the length of a single frame and the ratio of a DL section to a UL section, is provided via MAP information. In order to dynamically allocate resources to PSSs, an RAS may send different MAPs through each frame. In this case, a MAP may be divided into DL_MAP, containing DL transmission information, and UL_MAP, containing UL resource access authority. Here, DL_MAP can be defined as a Media Access Control (MAC) layer message that defines the symbol offset and sub-channel offset of a burst divided and multiplexed along the subchannel and time axes on a downlink by an RAS, and the numbers of symbols and sub-channels, that is, allocated resources. A frame number having a value varying depending on the frame is included in the DL_MAP. Next, the UL_MAP may be defined as a set of pieces of information that completely defines the access to a UL section. UL_MAP may include CID information. Furthermore, a uniquely defined preamble is present in the first symbol of a DL sub-frame, by which the PSS can be made aware of the start point of DL transmission. Furthermore, a cell Identification (ID) information and segment information are included in the preamble.
Meanwhile, in order for the mobile WiMax system analyzer to analyze the performance of a PSS, a signal generation unit for enabling the PSS to maintain DL synchronization is required. If the frame number of a DL signal does not increase, the PSS loses synchronization. The PSS sends a UL signal based on the received DL signal, and the signal analyzer acquires UL synchronization through the step of receiving the signal and estimating the start point of UL transmission and the step of causing frame numbers to coincide with each other. As a result, in order to acquire and analyze UL synchronization by the mobile WiMax system analyzer, a DL sub-frame having a frame number increasing in real time must be created with the help of the RAS, the PSS must be caused to acquire DL synchronization, and then the RAS must perform a network entry procedure in conjunction with the PSS, must be provided with timing synchronization for the start point of UL transmission, and must also be provided with a frame number.
As described above, in order to acquire and analyze UL synchronization for a PSS by a conventional mobile WiMax system analyzer, an RAS must be used. However, this scheme has problems in that it is not easy in practice to use the RAS for a PSS test, and in that the cost of the establishment of an analysis environment for the scheme is high.